The Internet comprises a large number of interconnected communications networks. In topological terms, the Internet comprises a large number of nodes which can communicate with each other. It is sometimes desirable for a Mobile Node to connect to the Internet to communicate with nodes in the Internet. A node with which the Mobile Node communicates is known as a Correspondent Node (CN). In practice, the Mobile Node has a number of Correspondent Nodes. The Mobile Node can be located in any number of modes of transport, for example: a train, a boat, an aircraft, a car. Alternatively, the Mobile Node may correspond to a moving human being, for example, a Personal Area Network.
As implied by the word “mobile”, the Mobile Node is not limited to a single topological point of attachment to the Internet. Instead, the Mobile Node can move between and connect to a number of topological points of attachment to the Internet. The Mobile Node is identified by a Home Address, the Home Address corresponding to an Internet Protocol (IP) address on a Home Link. The Home Link is a communications link with a router known as a Home Agent, the Home Link corresponding to an initial topological point of attachment to the Internet; a link with a router located at a topological point of attachment other than the initial topological point of attachment is known as a Foreign Link.
When the Mobile Node migrates from the initial topological point of attachment to the Internet to the Foreign Link, one of a number of routers on the Foreign Link assigns a Careof Address to the Mobile Node. The Careof Address is an IP address identifying the current topological point of attachment of the Mobile Node to the Internet.
Subsequent movements of the Mobile Node to other Foreign Links results in the allocation of respective new Careof Addresses. The Careof Address is registered with the Home Agent. In order to maintain continuous connectivity between a Correspondent Node and the Mobile Node, mobility management is required.
The Mobile-IPv4, the Mobile-IPv4 with route optimisation and the Mobile-IPv6 protocols devised by the Mobile-IP working group of the Internet Engineering Task Force (IETF) are designed to manage the mobility of the Mobile Node.
In order to optimise routing paths between the Correspondent Nodes and the Mobile Node, it is necessary to provide the Correspondent Nodes of the Mobile Node with the Careof Address of the Mobile Node.
Under the Mobile-IPv4 protocol, Correspondent Nodes are not aware of the Careof Address of the Mobile Node. Consequently, all traffic destined for the Mobile Node is routed via the Home Agent, the Home Agent redirecting the traffic destined for the Mobile Node to the current topological point of attachment of the Mobile Node to the foreign network using the Careof Address corresponding to the IP address of the router on the Foreign Link, known as a Foreign Agent, in the Mobile-IPv4 protocol. Under the Mobile-IPv4 protocol with route optimisation, the Careof Address of the Mobile Node is sent by the Home Agent to all the Correspondent Nodes of the Mobile Node, thereby ensuring that all traffic destined for the Mobile Node is sent by an optimal path between the Correspondent Nodes and the Mobile Node.
Instead of the Home Agent communicating the Careof Address to the Correspondent Nodes of the Mobile Node, the Mobile-IPv6 protocol requires the Careof Address of the Mobile Node to be sent by the Mobile Node itself to the Correspondent Nodes of the Mobile Node, again thereby ensuring that all traffic destined for the Mobile Node is sent by the optimal path between the Correspondent Nodes and the Mobile Node.
In the cases of Mobile-IPv4 with route optimisation and Mobile-IPv6, the Careof Address is communicated to the Correspondent Nodes of the Mobile Node by means of a message known as a “Binding Update” (BU). Under the Mobile-IPv4 with route optimisation and the Mobile-IPv6 protocols, BUs need to be periodically sent to each Correspondent Node of the Mobile Node.
The Mobile-IPv4 protocol is clearly inefficient in terms of routing, due to the triangular nature of the route taken by any data destined for the Mobile Node when the Mobile Node is connected to a Foreign Link. The Mobile-IPv4 protocol with route optimisation and the Mobile-IPv6 protocol, whilst being reasonably efficient in routing terms, begin to be inefficient in terms of signalling costs and bandwidth use when the number of Correspondent Nodes of the Mobile Node becomes large. As the number of Correspondent Nodes increases, the number of BUs correspondingly increases. Hence, for a large number of Correspondent Nodes of the Mobile Node, a risk exists of overloading the Internet with signalling messages, i.e. a Binding Update “explosion”.
Additionally, the above described protocols do not either: specifically support large mobile networks, or do not specifically support mobile networks at all. A mobile network is a number of interconnected nodes which move together relative to a fixed network, for example, the Internet. The Mobile-IPv4 with route optimisation and Mobile-IPv6 protocols do not mention support for mobile networks.
A way of using the above protocols to support mobile networks is to perceive the mobile network as a mobile router coupled to a number of nodes. Since the mobile router is an example of the Mobile Node, the mobile router can obtain a Careof Address for registration with the Home Agent. However, as the mobile network can contain hundreds of nodes, each having several Correspondent Nodes, the number of BUs which need to be transmitted is considerable and increases with growth of the mobile network. If the number of nodes forming the mobile network becomes too large, the number of BUs sent may again overload the network with signalling messages.
Also in the context of mobile networks, it is not clear from the Mobile-IPv4 protocol with route optimisation and the Mobile-IPv6 protocol whether the BUs are transmitted by the nodes forming the mobile network or the mobile router, further evidencing the fact that the above protocols have not been designed to support mobile networks. Transmission of BUs by the nodes forming the mobile network requires additional mechanisms to distribute the Careof Address obtained by the mobile router coupled to the mobile network. Also, authentication problems arise at the Correspondent Nodes when the BUs are transmitted by the mobile router.
In summary, the Mobile-IPv4 protocol is inefficient in terms of bandwidth use, because data is not routed by an optimal path between the Correspondent Node and the Mobile Node. Mobile-IPv4 with route optimisation and Mobile-IPv6 do support optimal routing by providing the IP address identifying the current topological point of attachment of the Mobile Node to the Internet, but do not cope well when the number of Correspondent Nodes is large and/or the Mobile Node corresponds to a mobile network formed by a large number of nodes.
The present invention to obviates, or at least mitigates, the disadvantages associated with supporting Mobile Nodes and mobile networks in an IP environment.